Blew a 4-inch slab pour last Tuesday. Still trying to figure out what went wrong.

Had a job at a driveway in Tulsa where the whole thing cracked straight down the middle 6 hours after finishing. I used the exact same mix I always use, 4000 PSI with fiber mesh, and the temp was fine at 72 degrees. My only guess is the subgrade wasn't damp enough when I poured, but I didn't think it would matter that much. Has anyone else had a fresh slab crack that fast from dry ground underneath?

2 comments

2 Comments

abbyc338d agoMost Upvoted

4000 PSI with fiber should NOT crack through in 6 hours no matter what the subgrade is doing. That's a full structural failure, not a cosmetic control joint issue. If you're seeing a single crack straight down the middle that fast, you have a subgrade compaction problem or the ground was actually WET instead of just dry.

the_tara9d ago

Is it actually that big of a deal though? I mean, yeah, it cracked, but if it's just a single line down the middle and the slab is still sitting solid, that's pretty normal for a driveway. A lot of guys would just cut a control joint right there later and call it a day. Plus, if you were using 4000 PSI with fiber and the temp was fine, I wouldn't stress too much over the subgrade being dry. It could just be the ground settling a bit or a weak spot in the base. Honestly, unless it's lifting or starting to crumble, I'd just patch it and move on lol.